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  • 1.
    Alexiadis, Alessio
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Dudukovic, M. P.
    Ramachandran, P.
    Cornell, Ann
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    On the stability of the flow in multi-channel electrochemical systems2012In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 42, no 9, p. 679-687Article in journal (Refereed)
    Abstract [en]

    The importance of the fluid dynamics in the modelling of electrochemical systems is often underestimated. The knowledge of the flow velocity pattern in an electrochemical cell, in fact, can allow us to associate certain electrochemical reactions with specific fluid patterns to maximize the yield of some reaction and, conversely, to minimize unwanted or side reactions. The correct evaluation of the convective term in the Nernst-Planck equation, however, requires the solution of the so-called Navier-Stokes equations, and computational fluid dynamics (CFD) is today the established method to numerically solve these equations. In this work, a CFD model is employed to show that the gas-liquid flow pattern can be remarkably different in a single channel or in a multi-channel gas-evolving electrochemical system. In the single channel, in fact, under certain conditions, vortices and recirculation regions can appear in the flow, which does not appear in the multi-channel case. The reason of this difference is found in the uneven distribution of the small bubbles in the two cases. Additionally, a second, simplified, model of the flow is discussed to show how a higher concentration of small bubbles in the single channel system can destabilize the flow.

  • 2.
    Behm, Mårten
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Electrochemical production of polysulfides and sodium hydroxide from while liquor .2. Electrolysis in a laboratory scale flow cell1997In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 27, no 5, p. 519-528Article in journal (Refereed)
    Abstract [en]

    Electrochemical production of polysulfide-containing white liquor and pure sodium hydroxide solution was investigated at 90 degrees C in a laboratory scale flow cell. A mixed iridium-tantalum oxide coated titanium electrode was used as the anode and the two electrolyte compartments were separated by a cation-exchange membrane. The process was demonstrated at current densities up to 5 kA m(-2), resulting in high current efficiencies for both products. The previously reported autocatalytic effect of polysulfide ions was confirmed, and its technical implications on the use of three-dimensional electrodes were demonstrated and discussed. The current efficiency was found to depend strongly on the degree of conversion of sulfur(-II) to sulfur(0). The anode material showed favourable properties, with respect to activity and selectivity, but suffered from limited durability.

  • 3.
    Behm, Mårten
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Electrochemical production of polysulfides and sodium hydroxide from white liquor .1. Experiments with rotating disc and ring-disc electrodes1997In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 27, no 5, p. 507-518Article in journal (Refereed)
    Abstract [en]

    Electrochemical oxidation of white liquor in a membrane cell is a process of great potential for the pulp and paper industry. The process produces polysulfide-containing white liquor in the anode chamber, and pure sodium hydroxide solution in the cathode chamber. The anode reaction has been investigated using cyclic voltammetry at temperatures between 25 and 90 degrees C on rotating disc and ring-disc electrodes. It was further investigated using chronoamperometry on rotating disc electrodes at 90 degrees C. The experiments, which were mainly run in dilute alkaline sulfide solutions, using platinum electrodes, show that the electrochemical production of polysulfide ions, at lower anode potentials (-0.1 to +0.1 V vs SCE), proceeds via formation of elemental sulfur on the electrode surface. The sulfur is dissolved by hydrosulfide and polysulfide ions producing (longer-chain) polysulfide ions. The rate of dissolution, and thus the overall reaction rate, increases strongly with temperature. Polysulfide ions have an autocatalytic effect on the anode reaction due to their ability to dissolve adsorbed sulfur. At higher anode potentials (greater than or equal to 0.2 V vs SCE), a change of reaction mechanism is observed. In this region the reaction rate depends on electrode potential and is not catalysed by polysulfide ions.

  • 4.
    Behm, Mårten
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Graphite as anode material for the electrochemical production of polysulfide ions in white liquor1999In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 29, no 4, p. 521-524Article in journal (Refereed)
  • 5. Borg, K. I.
    et al.
    Birgersson, K. E.
    Bark, Fritz H.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Effects of non-linear kinetics on free convection in an electrochemical cell with a porous separator2007In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 37, no 11, p. 1287-1302Article in journal (Refereed)
    Abstract [en]

    The spatial evolution of the ionic concentration of an electrolyte in an isothermal electrochemical cell with a porous separator between the electrodes was investigated for large values of Rayleigh number. The reaction kinetics were described by the Butler-Volmer equation. The full problem, involving the coupled partial differential equations describing the velocity field, the ionic concentration, and the electric potential, was reduced by means of regular and singular perturbation theory, to a simplified evolution equation, coupled with a transcendental function for the ionic concentration and electric potential; the solution was found to agree well with the numerical solution of the full problem. In the limit of large and small cell voltages, closed analytical solutions were secured for the concentration, potential, and overall current density.

  • 6. Bouzek, K.
    et al.
    Cornell, Ann M.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering.
    Rodrigo, M. A.
    Preface on the special issue 2nd workshop on electrochemical engineering: new bridges for a new knowledge on electrochemical engineering2018In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 48, no 12, p. 1305-1306Article in journal (Refereed)
  • 7.
    Cornell, Ann
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Applied Electrochemistry.
    Rodrigo, Manuel
    Univ Castilla La Mancha, Dept Chem Engn, Ciudad Real, Spain..
    Bouzek, Karel
    Univ Chem & Technol Prague, Prague, Czech Republic..
    Special Issue: 11th European Symposium in Electrochemical Engineering (ESEE 11) Foreword2018In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 48, no 6, p. 559-560Article in journal (Refereed)
  • 8. Dannenberg, K.
    et al.
    Ekdunge, P.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Mathematical model of the PEMFC2000In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 30, no 12, p. 1377-1387Article in journal (Refereed)
    Abstract [en]

    A two-dimensional along-the-channel mass and heat transfer model for a proton exchange membrane fuel cell (PEMFC) is described. The model is used for calculation of cell performance (i.e., cell voltage against current density), ohmic resistance and water profile in the membrane, current distribution and variation of temperature along the gas channels. The following fuel cell regions are considered: gas channels, electrode backings and active layers at the anode and cathode side, and a proton exchange membrane. The model includes mass transfer in the gas channels and electrode gas backings, water transport in the membrane, electrode kinetics and heat transfer. Temperature in the cell is assumed to vary only along the gas channels, which means that it is the same at the anode and cathode and in the solid phase at a specified value of the channel coordinate. Electrode kinetics are considered only at the cathode, where major losses occur, whereas the anode potential is assumed to be equal to its equilibrium value. An agglomerate approach is used for the description of the active layer of the cathode. Simulations are carried out for different humidities of inlet gases, several different stoichiometric amounts of reactants and cooling media (air, water) with different heat transfer coefficients. Analysis of the results showed that the best performance of the PEMFC was obtained for well-humidified gases at conditions close to isothermal and at a stoichiometry of gases only somewhat higher than that corresponding to complete reactant consumption.

  • 9.
    Fontes, Eduardo
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Lagergren, Carina
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Simonsson, Daniel
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Influence of gas phase mass transfer limitations on molten carbonate fuel cell cathodes1997In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 27, no 10, p. 1149-1156Article in journal (Refereed)
    Abstract [en]

    The purpose of this paper is to elucidate to what extent mass transfer limitations in the gas phase affect the performance of porous molten carbonate fuel cell cathodes. Experimental data from porous nickel oxide cathodes and calculated data are presented. One and two-dimensional models for the current collector and electrode region have been used. Shielding effects of the current collector are taken into account. The mass balance in the gas phase is taken into account by using the Stefan-Maxwell equation. For standard gas composition and normal operating current density, the effect of gas-phase diffusion is small. The diffusion in the gaseous phase must be considered at operation at higher current densities. For low oxygen partial pressures, the influence of mass transfer limitations is large, even at low current densities. To eliminate the influence of conversion on polarization curves recorded on laboratory cell units, measurements should always be performed with a five to tenfold stoichiometric excess of oxygen. Two-dimensional calculations show rather large concentration gradients in directions parallel to the current collector. However, the influence on electrode performance is still small, which is explained by the fact that most of the current is produced close to the electrolyte matrix.

  • 10. Gurniki, F.
    et al.
    Fukagata, K.
    Zahrai, S.
    Bark, Fritz H.
    KTH, Superseded Departments, Mechanics.
    LES of turbulent channel flow of a binary electrolyte2000In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 30, no 12, p. 1335-1343Article in journal (Refereed)
    Abstract [en]

    The turbulent diffusion boundary layer in a binary electrolyte was considered at Schmidt numbers of 1, 10 and 100 and exchange current densities between 10(-4) A m(-2) and 10(-2) A m(-2). A numerical scheme was developed for efficient investigation of the dynamics by means of large eddy simulations. The methodology was examined by detailed comparisons with documented data from earlier large eddy and direct numerical simulations and good agreement was found. Application of the methodology to electrochemical mass transfer indicated that the exchange current density seems to have negligible effect on the mean concentration profile but it influences the structure of the fluctuating field in a visible manner.

  • 11.
    Gustavsson, John
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Nylen, Linda
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Cornell, Ann
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Rare earth metal salts as potential alternatives to Cr(VI) in the chlorate process2010In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 40, no 8, p. 1529-1536Article in journal (Refereed)
    Abstract [en]

    Chromate is today added to industrial chlorate electrolyte, where it forms a thin cathode film of chromium hydroxide that hinders unwanted reduction of hypochlorite and chlorate. The aim of this study was to investigate rare earth metal (REM) ions as an environmentally friendly alternative to the toxic chromate addition. Potential sweeps and iR-corrected polarisation curves were recorded using rotating disc electrodes of iron and gold. Addition of Y(III), La(III) or Sm(III) to 5 M NaCl at 70 A degrees C suppressed hypochlorite reduction. Activation of hydrogen evolution by REM ion addition to 0.5 M NaCl was more significant at 25 A degrees C than at 50 and 70 A degrees C. Increasing the chloride concentration to 5 M had a detrimental effect on this activation. The major problem in replacing chromate with REM salts is the poor solubility of REM ions at normal chlorate process conditions, and therefore REM salts are not a realistic alternative to chromate addition.

  • 12.
    Hedberg, Yolanda
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Lundin, Maria
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Jacksén, Johan
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Emmer, Åsa
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Analytical Chemistry.
    Blomberg, Eva
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Wallinder, Inger Odnevall
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Chromium-protein complexation studies by adsorptive cathodic stripping voltammetry and MALDI-TOF-MS2012In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 42, no 5, p. 349-358Article in journal (Refereed)
    Abstract [en]

    A methodology using stripping voltammetry has been elaborated to enable sensitive and reliable protein-chromium complexation measurements. Disturbing effects caused by adsorption of proteins on the mercury electrode were addressed. At low concentrations of proteins (< 60-85 nM), chromium-protein complexation measurements were possible. Chromium(VI) complexation was quantitatively determined using differently sized, charged, and structured proteins: serum albumin (human and bovine), lysozyme, and mucin. Generated results showed a strong relation between complexation and protein size, concentration, and the number of amino acids per protein mass. Complexation increased nonlinearly with increasing protein concentrations. The nature of this complexation was based on weak interactions judged from combined results with MALDI-TOF-MS and adsorptive cathodic stripping voltammetry.

  • 13.
    Ipek, Nulifer
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Faxén Laboratory. KTH, School of Engineering Sciences (SCI), Mechanics.
    Lior, Noam
    University of Pennsylvania, Dept. Mech. Eng. and Appl. Mechanics.
    Vynnycky, Michael
    KTH, School of Engineering Sciences (SCI), Centres, Faxén Laboratory. KTH, School of Engineering Sciences (SCI), Mechanics.
    Bark, Fritz H.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Mechanics of Industrial Processes.
    Numerical and experimental study of the effect of gas evolution in electrolytic pickling2006In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 36, no 12, p. 1367-1379Article in journal (Refereed)
    Abstract [en]

    As part of a progressive approach to model the electrolytic pickling process, this paper focuses on the important aspect of hydrogen and oxygen gas evolution on the electrodes and on the steel strip being pickled. The system considered consists of type 316 stainless steel pickled in aqueous sodium sulphate, with lead anodes and stainless steel cathodes. The mathematical model is two-dimensional steady-state, and includes the differential equations describing the effect of migration, giving the potential and current fields, and the Tafel kinetic rate expressions for hydrogen and oxygen gas generation. Experiments were conducted to obtain a better understanding of the process and for model validation. Good agreement between the experimental measurements of the global current efficiency and the model predictions was obtained.

  • 14.
    Lin, Yuan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Shiomi, Junichiro
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Maruyama, Shigeo
    Department of Mechanical Engineering, The University of Tokyo.
    Amberg, Gustav
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Brandner, Birgit D.
    YKI, Ytkemiska Institute AB/Institute for Surface Chemistry.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Dielectric properties of water inside single-walled carbon nanotubesIn: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838Article in journal (Other academic)
  • 15. Noponen, M.
    et al.
    Ihonen, Jari
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Lundblad, Anders
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Current distribution measurements in a PEFC with net flow geometry2004In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 34, no 3, p. 255-262Article in journal (Refereed)
    Abstract [en]

    A measurement system for current distribution mapping for a PEFC has been developed. The segmented anode is constructed so as to have high thermal conductivity in order to prevent the formation of large temperature gradients between the electrodes. The construction is therefore feasible for use at high current densities. Both segmented and unsegmented gas diffusion layers are used. The effect of inlet humidification and gas composition at the cathode side is studied. In addition, two different flow geometries are studied. The results show that the measurement system is able to distinguish between current distribution originating from differences in proton conductivity, species concentration and gas diffusion layer properties.

  • 16. Nordlund, J.
    et al.
    Roessler, A.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    The influence of electrode morphology on the performance of a DMFC anode2002In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 32, no 3, p. 259-265Article in journal (Refereed)
    Abstract [en]

    For low concentrations of methanol, mass transfer in the electrode is a limiting parameter for the direct methanol fuel cell (DMFC). To improve mass transfer, it is possible to induce convection in the gas backing layer or even in the porous electrode. In this study electrodes with different amounts of PTFE were compared to observe the influence of morphology on the anode performance. The hypothesis was that adding PTFE to the anode may make the morphology more favourable for carbon dioxide to evolve as a gas by creating the necessary pore sizes. Electrode performance was characterized electrochemically and the anode layer structure was studied using SEM, Hg-porosimetry and the van der Pauw method for measuring electric conductivity. Pores smaller than 0.04 mum were unaffected by adding PTFE while the volume fraction of pores of 0.04-1.0 mum diameter increased. Electrodes with 50% PTFE also performed as nonhydrophobized, despite the much higher ohmic losses and thickness. This implies that, above a certain amount, adding PTFE has a positive effect and that optimizing the electrode with PTFE may give better performance than electrodes without PTFE. The results suggest that gas evolves within the electrode, giving improved mass transfer in the liquid phase.

  • 17.
    Nordlund, Joakim
    et al.
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Picard, C
    Birgersson, Erik
    KTH, Superseded Departments, Mechanics.
    Vynnycky, Michael
    KTH, Superseded Departments, Mechanics.
    Lindbergh, Göran
    KTH, Superseded Departments, Chemical Engineering and Technology.
    The design and usage of a visual direct methanol fuel cell2004In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 34, no 8, p. 763-770Article in journal (Refereed)
    Abstract [en]

    In order to better understand the influence of gas evolution on the performance of the direct methanol fuel cell ( DMFC) anode, a visual DMFC, comprising of a transparent anode and a cathode endplate with an integrated heat exchanger, and a picture analysis methodology were developed. The result was an inexpensive, but very powerful, tool for analyzing the role of two-phase flow. An important finding is that gas bubbles do not appear uniformly throughout the fluid flow matrix, but rather only at a few active sites. Another important finding is that the gas saturation ( volume fraction of gas/volume fraction of liquid) increases along the streamwise direction.

  • 18.
    Nylén, Linda
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Cornell, Ann M.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Effects of electrolyte parameters on the iron/steel cathode potential in the chlorate process2009In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 39, no 1, p. 71-81Article in journal (Refereed)
    Abstract [en]

    This study focuses on how different electrolyte parameters of the chlorate process affect the cathode potential for hydrogen evolution on iron in a wide current-density range. The varied parameters were pH, temperature, mass transport conditions and the ionic concentrations of chloride, chlorate, chromate and hypochlorite. At lower current densities, where cathodic protection of the electrode material is important, the pH buffering capacity of the electrolyte influenced the potential to a large extent. It could be concluded that none of the electrolyte parameters had any major effects (< 50 mV) on the chlorate-cathode potential at industrially relevant current densities (around 3 kA m(-2)). Certainly, there is more voltage to gain from changing the cathode material than from modifying the electrolyte composition. This is exemplified by experiments on steel corroded from operation in a chlorate plant, which exhibits significantly higher activity for hydrogen evolution than polished steel or iron.

  • 19. Olivas, P.
    et al.
    Alemany, A.
    Bark, Fritz H.
    KTH, Superseded Departments, Mechanics.
    Electromagnetic control of electroplating of a cylinder in forced convection2004In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 34, no 1, p. 19-30Article in journal (Refereed)
    Abstract [en]

    Continuous electrodeposition on a cylindrical cathode, e. g. electrodeposition of gold on electrical connectors, is usually characterized by an undesirable non- homogeneity of the deposit thickness. This has been observed in industrial applications. Numerical simulations have shown very good agreement with observations. This paper deals with the possibility of improving the homogeneity of the deposit thickness by a magnetic field that is parallel to the axis of the cylinder. The electromagnetic volume force generated by such a magnetic field may set up a swirling motion around the cylinder. By controlling the force density it is possible to control the thickness of the diffusive layer and consequently the mass transfer. The magnetic field can be optimized with respect to strength, spatial extent and variation with time. It is shown that a strong alternating magnetic field of low frequency gives a nearly homogeneous deposit.

  • 20.
    Vernersson, Thomas
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    A model for mass transport in the electrolyte membrane of a DMFC2007In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 37, no 4, p. 429-438Article in journal (Refereed)
    Abstract [en]

    A steady state model for multicomponent mass transport was derived for the direct methanol fuel cell membrane. Data for development and validation of the model was taken both from experiments and literature. The experimental data was collected in a polarisation cell, where mass transport of methanol across the electrolyte membrane was measured through a potentiostatic method. The results from modelling and experiments showed good agreement. The model was capable of describing the non-linear response in mass transport to increased methanol feed concentration. The model also accurately described the change in membrane conductivity with methanol concentration. From the model transport equations, it was also possible to derive some characteristic transport parameters, namely the electro osmotic drag of both water and methanol, diffusive drag of water and methanol, and effective, concentration dependent, diffusion coefficients for methanol and water.

  • 21.
    Wesselmark, Maria
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Lagergren, Carina
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Lindbergh, Göran
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Methanol and formic acid oxidation in zinc electrowinning under process conditions2008In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 38, no 1, p. 17-24Article in journal (Refereed)
    Abstract [en]

    The possibility of using methanol or formic acid oxidation as the anode process in zinc electrowinning was examined. The activity for methanol and formic acid oxidation on Pt coated high surface area electrodes was investigated over 36 h, at a current density used in industry. The activity could be maintained at a constant potential level in a synthetic electrowinning electrolyte if the current was reversed for short periods. During the tests, the anode potential was, more than 1.2 V below the potential for the oxygen evolving lead anodes used in modern zinc electrowinning. The lowered anode potential would lead to a significant energy reduction. However, tests in industrial electrolyte resulted in a very low activity for both methanol and formic acid oxidation. The low activity was shown to be caused mainly by chloride impurities. A reduction of the chloride content below 10(-5) M is needed in order to obtain sufficient activity for methanol oxidation on Pt for use in zinc electrowinning. Pt and PtRu electrodes were compared regarding their activity for methanol oxidation and the latter was shown to be more affected by chloride impurities. However, at a potential of 0.7 V vs NHE, with a chloride content of 10(-4) M, formic acid oxidation on PtRu gives the highest current density.

  • 22. Wulff, Josefin
    et al.
    Cornell, Ann M.
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
    Cathodic current efficiency in the chlorate process2007In: Journal of Applied Electrochemistry, ISSN 0021-891X, E-ISSN 1572-8838, Vol. 37, no 1, p. 181-186Article in journal (Refereed)
    Abstract [en]

    Sodium chlorate is produced in undivided electrolysis cells. Hydrogen is evolved on the cathodes, usually made of steel, while chloride ions are oxidised to chlorine on the anodes, usually DSA (R) s. Parasitic cathodic reactions, lowering the cathodic current efficiency (CE), are the reduction of hypochlorite and chlorate ions. These reactions are suppressed by the addition of Cr(VI) to the electrolyte. In this work the effects that time of the electrolysis, chromate concentration and interruption of the electrolysis process have on CE has been investigated. New steel, as well as steel samples cut from cathodes used in a chlorate plant, were used as cathode material. Laboratory experiments in a divided cell were made to determine the rate of hydrogen production, and thereby indirectly CE, at varying operating conditions. It was found that the chromate concentration is important for the CE in the range 0.5-6 g l(-1) Na2Cr2O7. The CE was higher on new steel than on the used steel, which had a more corroded and inhomogeneous surface. When starting the electrolysis the CE was initially low, at a value depending on the operating conditions, but increased with time of polarisation. The time to reach an approximate steady CE was generally in the order of hours. Electrolysis shut downs in the presence of hypochlorite (<= 3 g l(-1) NaClO) resulted in corrosion of iron and a low CE when restarting the process. After one such corrosion shut down the new steel showed as low CE as the used steel. When restarting the electrolysis after a shut down without hypochlorite the CE was higher than before the shut down. Current densities of a simulated bipolar plate during a shut down were measured to 50-150 A m(-2), resulting from oxidation of steel and reduction of oxy chlorides on the catalytic DSA (R) electrode.

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